Peel the potatoes and then slice them in ½ cm slices (1/4").
Peel and chop the onions.
Put the cream, milk, salt, pepper, garlic, onions and potatoes in a pot.
Cook up on medium heat for about 5 minutes (after they are simmering), continue until the potatoes are flexible. (they should not become mushy! Whoa! Stop Now!)
Dump everything into a baking dish (casserole dish).
(at this point the dish can be saved for some days in the fridge)
Spread the grated cheese on top.
Bake at 225°C or 350°F until golden brown.
approx. 25 minutes for warm potatoes, 35 minutes if it has been chilled
Cool a bit before serving.
Recipe by at https://trotsig.com/potatoes-au-gratin/